The electrical rotating tools in the prior arts commonly utilize electricity as a power source and have different designs, including plug type, recharge type, and plug/recharge type. The electric tool can serve as an electric drill when the chuck of the electric tool clamps a drill, or an electric screwdriver when the chuck of the electric tool clamps a driver. The plug type of electric tool may provide more driving force when the electric socket is available. The recharge type of electric tool, however, provides a convenient selection when the electric socket is not available or the electric socket is too far to connect with the wire. The recharge type of electric tool is sometimes not available when the stored electricity is not sufficient to drive the drill or the screwdriver, and can not recover by recharging at once. The plug type of electric tool will also be not available when the power is shut down. Therefore, the electric tool has to be operated by hand in such conditions. However, the active gear of the traditional electric tool is generally engaged with the gear set, which is engaged with the passive gear connected with the central axle. The passive gear becomes an active gear when the electric tool is forced to rotate by hand to serve as a hand drill or a hand screwdriver. The gear set is further connected with the active gear of the driving motor shaft. As a result, the drill or the screwdriver becomes idling, i.e.; the electric tool can not operate by hand. Moreover, although several improved electric tools, which prevent the output shaft from counter rotating, have been developed, e.g., Taiwan Patent No. 87218052, the structure is more complicated and difficult to manufacture. The present invention, thus, provides an electric tool with an improved locking device to overcome all the shortcomings in the prior arts.